Re: Define nr of measures per system

[Urs Liska]

Am 06.03.2018 um 18:47 schrieb Kieren MacMillan:
> Hi Omri,
>
> > Another beginner question, but can't seem to find the answer in the 
> > documentation:
> > is it possible to define a constant number of measures per staff system?
> There is no dead-simple, built-in way… but there are many ways of accomplishing 
> what you want, each with pros and cons depending on exactly what functionality 
> and flexibility you want.
>
> For a constant number of measures per system, my favourite is David K's 
> \bar-keeper, which I’ve shown in the snippet below.
>
> (Aside: I’m not sure why this isn’t in the main base code… Given that David K 
> coded it, I imagine it’s the most elegant solution possible to the problem he 
> was tasked to solve. And it is a function that many, many users would 
> appreciate having access to.)


Another approach that works well (and could easily be enhanced if there 
is interest) would involve openLilyLib packages, namely the page-layout 
package. Internally this uses the edition-engraver to "inject" breaks at 
specific positions which are targeting "measures", regardles of time 
signatures.

The current interface would be (skipping the installation and set-up here):

%%%
\include "oll-core/package.ily"
\loadPackage \with {
  modules = conditional-breaks
}
page-layout
\registerBreakSet my-breaks
\setBreaks my-breaks line-breaks 5.8.13.17.21.25
\applyconditionalBreaks my-breaks
%%%

This would apply line breaks at the measures given in the dot-separated 
list.

What I think would be a useful enhancement would be a function that adds 
a regular list of breaks, possibly limited to a section, for example with

\setBreaks my-breaks line-breaks 5.12.17.23.51
\addRegularBreaks my-breaks line-breaks 26 4 6

which would insert "6" breaks after "4" measures each, starting with 
"26", i.e. 26.30.34.38.42.46
Other interfaces could be thought of, in particular ways that apply the 
regular measures globally (i.e. not starting at a specific point) or 
"from here throughout the end".

Is this something I should add to the page-layout package?

Urs

> Hope this helps!
> Kieren.
>
> %%%  SNIPPET BEGINS
> \version "2.19"
>
> #(define (index-list? x)
>    (and (list? x)
>         (every index? x)))
>
> #(define (index-pattern numbers)
>    "Convert an `index pattern' into a circular list.  Zeros are removed,
> with the last zero preceding the part of the list that should become
> circular.  If that list part is empty, the resulting list has no circular
> end.  Without any zero, the whole list is turned into a circular one."
>    (define (creverse! x y)
>      "Reverse both x and y, make y circular and append to x."
>      (if (pair? y)
>          (let* ((rev-y (reverse! y))
>                 (rev-x (reverse! x rev-y)))
>            (set-cdr! y rev-y)
>            rev-x)
>          (reverse! x y)))
>    (let loop ((non-reps '()) (reps '()) (rest numbers))
>      (cond ((null? rest) (creverse! non-reps reps))
>            ((zero? (car rest))
>             (loop (append! reps non-reps) '() (cdr rest)))
>            ((index? (car rest))
>             (loop non-reps (cons (car rest) reps) (cdr rest)))
>            (else (ly:input-warning (*location*)
>                                    (_ "Not an index: ~a") (car rest))
>                  (loop non-reps reps (cdr rest))))))
>
> bar-keeper =
> #(define-scheme-function (numbers) (index-list?)
>    "Create a context mod for consisting a Timing-level engraver
> breaking after bar group lengths specified in the list.  If the list
> is exhausted, it starts over from the start or from after a 0 marker
> contained in the list.  If the list @emph{ends} address@hidden, line
> breaking reverts to normal after using up the list."
>    (ly:make-context-mod
>     `((consists
>        ,(lambda (c)
>           (let ((target #f) (numbers (index-pattern numbers)))
>             (make-engraver
>              (acknowledgers
>               ((paper-column-interface eng grob from)
>                (and (pair? numbers)
>                     (ly:grob-property grob 'non-musical #f)
>                     (let ((bar (ly:context-property (ly:translator-context eng)
>                                                     'internalBarNumber)))
>                       (if (not target)
>                           (set! target bar)
>                           (set! (ly:grob-property grob 'line-break-permission)
>                                 (and (>= bar (+ target (car numbers)))
>                                      (begin
>                                        (set! target (+ target (car numbers)))
>                                        (set! numbers (cdr numbers))
>                                        'force)))))))))))))))
>
>
> \score {
>    \new Score \with \bar-keeper 4 {
>      \repeat unfold 100 { c''4 }
>    }
> }
> %%%  SNIPPET ENDS
> ________________________________
>
> Kieren MacMillan, composer
> ‣ website: www.kierenmacmillan.info
> ‣ email: address@hidden
>
>
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